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Статья

Evolution of superconducting gaps in Th-substituted Sm1-xThxOFeAs studied by multiple Andreev reflection spectroscopy

Kuzmicheva T., Kuzmichev S., Pervakov K., Pudalov V., Zhigadlo N.

Using intrinsic multiple Andreev reflections effect spectroscopy, we studied SnS contacts in the layered oxypnictide superconductors Sm1-xThxOFeAs with various thorium doping and critical temperatures TC=21-54 K. We observe a scaling between both superconducting gaps and TC. The determined BCS ratio for the large gap 2ΔL/kBTC=5.0-5.7 and its eigen-BCS ratio (in a hypothetical case of zero interband coupling) 2ΔL/kBTCL=4.1-4.6 both exceeding the weak-coupling limit 3.52, and for the small gap 2ΔS/kBTC=1.2-1.6, remain nearly constant within all the TC range studied. The temperature dependences ΔL,S(T) agree well with a two-band BCS-like Moskalenko and Suhl model. We prove intraband coupling to be stronger than interband coupling, whereas Coulomb repulsion constants μ∗ are finite in Sm-based oxypnictides.